Rosenbluth separation of the $\pi^0$ electroproduction cross section

TL;DR

This study measures the $^0$ electroproduction cross section at specific kinematics, using Rosenbluth separation, revealing dominance of the transverse component and potential access to transversity GPDs, challenging perturbative QCD predictions.

Contribution

It provides the first Rosenbluth separation of $^0$ electroproduction cross sections at Jefferson Lab, highlighting the significance of transversity GPDs in the process.

Findings

Cross section dominated by transverse component.

Indication of non-zero longitudinal contribution.

Agreement with models involving transversity GPDs.

Abstract

We present deeply virtual $\pi^0$ electroproduction cross-section measurements at $x_B$=0.36 and three different $Q^2$--values ranging from 1.5 to 2 GeV$^2$, obtained from experiment E07-007 that ran in the Hall A at Jefferson Lab. The Rosenbluth technique was used to separate the longitudinal and transverse responses. Results demonstrate that the cross section is dominated by its transverse component, and thus is far from the asymptotic limit predicted by perturbative Quantum Chromodynamics. An indication of a non-zero longitudinal contribution is provided by the interference term $\sigma_{LT}$ also measured. Results are compared with several models based on the leading twist approach of Generalized Parton Distributions (GPDs). In particular, a fair agreement is obtained with models where the scattering amplitude is described by a convolution of chiral-odd (transversity) GPDs of the nucleon with the twist-3 pion distribution amplitude. Therefore, neutral pion electroproduction may offer the exciting possibility of accessing transversity GPDs through experiment.